1. Field of the Invention
The invention relates generally to a technique for transferring information from one storage device to another storage device in a plurality of storage devices connected via a network.
2. Description of Related Art
A storage device typified by a disk array device logically divides a storage area of a disk device in the storage device and provides the divided storage areas as volumes (logical storage areas) to a host computer. When such a storage device is connected to a network, the host computer is connected to the storage device via the network to write-access and read-access to the volumes. As an example of a storage device that provides volumes to the host computer via a network, a NAS (Network Attached Storage) device is well known. The NAS device runs an OS (Operating System) and a file system, keeps information about files and directories stored in each volume, and inputs or outputs a file(s) in response to a request from the host computer.
When the performance or capacity of such a NAS system becomes insufficient, a possible solution to this problem would be to transfer data in the existing NAS device to a new NAS device to use the data from the existing NAS device in the new NAS device. This operation is referred to as data transfer between storage devices.
As a method for transferring data between NAS devices, a method for transferring a file by creating a hierarchical structure of the directories stored in an existing NAS device (i.e., a directory tree) in advance in a new NAS device and then transferring a file from the existing NAS system to the new NAS system in response to an access request from a host system has been disclosed (see JP 2004-46661 A).
There has also been proposed another method by which, even if access to a file that has not been transferred to the new NAS device is requested when transferring files from the existing NAS device to the new NAS device, the requested file is immediately identified on the file system of the existing NAS device storing the file, data is obtained from the existing NAS device and provided to a client, and a file providing service is transferred from the existing NAS device to the new NAS device in a relatively short time (see JP2006-39814 A).
OSs and file systems of NAS devices may differ depending on the type of the NAS devices. Due to that difference, for example, the maximum full path length of a directory tree that can be handled by a NAS device may be different. Therefore, when the maximum full path length of a directory tree that can be handled by the existing NAS device is longer than that in the new NAS device, the directory tree in the existing NAS device may not be able to be created in the new NAS device. Accordingly, an operator has to check in advance the directory structure of the existing NAS device and see whether or not the directory structure can be created in the new NAS device. If it is determined that the directory structure cannot be created in the new NAS device, the operator has to change the directory structure of the existing NAS device before the transfer, which increases the operator's workload.
Meanwhile, when a user of the NAS devices uses a desired file or directory, the user has to check whether or not the desired file or directory exists. Accordingly, just changing the directory structure of the existing NAS device would not allow the user to understand the details of the change, and would increase the user's workload when retrieving files or directories.